1. Field of the Invention
The present general inventive concept relates to an ink composition of inkjet recording, and more particularly, to an ink composition of inkjet recording, wherein the ink composition may prevent low-quality image printing caused by low ink-refill balance in a thermal inkjet recording apparatus.
2. Description of the Related Art
In an inkjet recording method, an image composed of a plurality of “dots” is recorded by ejecting ink droplets onto a printing medium from nozzles formed on a printhead of an inkjet printer. Inkjet printing is less expensive than other printing methods, a printing quality is high, and a color image can be easily formed. Ink used in inkjet printing is manufactured by dissolving or dispersing a water-soluble dye or a pigment in a solvent that contains water and selectively a water-miscible organic solvent. If necessary, an additive, for example, a surfactant, may be added to the solvent.
Inkjet printers may be classified into two types according to an ejection method of the ink droplets. A first type is a piezoelectric type that ejects ink by using a piezoelectric device and the second type is a thermal type that ejects ink by using a heat generating device.
The thermal type inkjet printer includes an inkjet printhead having a heat generating device that is installed in an ink chamber to heat ink and a driving circuit, such as a logic integrated circuit, to drive the heat generation device. Ink in the ink chamber generates bubbles by being locally heated by the heat generating device. As a result, ink droplets are formed in the ink chamber, and are ejected onto a printing medium through nozzles. In order to fill an empty space generated in the ink chamber due to the ink ejection, fresh ink must be supplied to the ink chamber from an ink tank through a supply line. At this point, if an ink-refill balance is low, low-quality image printing can occur when an image printing operation is consecutively performed. However, in order to address this problem, a fluidity of the ink in a channel formed between the ink chamber and the ink tank may be improved by modifying a channel structure design or changing a composition of the ink.
Due to the low ink-refill balance, a shortage of ink may occur in the ink chamber. In this case, when the ink is consecutively ejected, a cooling operation of a surface of the inkjet printhead may not be achieved, and thus, a surface passivation layer of the heat generating device may be damaged. The damage of the surface passivation layer can cause minute holes in a surface of a resistor, and thus, a lifetime of the resistor is reduced. If ink ejection is performed numerous times, the surface passivation layer may be corroded due to oxidation by cavitation and a chemical reaction with the high temperature ink. The corroded surface passivation layer damages an electrical insulating film, and, as a result, a circuit that supplies power to the resistor may be disconnected or a thermal conductivity of the resistor is reduced, thereby reducing a stability of an ink ejection velocity.
In order to eject dots at accurate positions on a recording medium, a variation in the ejection velocity in each of the nozzles, or between the nozzles, must be minimized. A dot position error reduces the quality of a printed image. When a volume of the ink droplets is small, the dot position error is easily noticed. However, in order to further increase a printing resolution, it is necessary to reduce a size of the ejected ink droplets. Also, a lifetime of the inkjet printhead must be increased in order to reduce costs associated therewith. However, if a normal ink-refill balance is not performed, ink that is to be supplied to the ink chamber may not be sufficient. In this case, ink droplets ejected on a recording medium may be small and may result in an ejection stability problem due to an excessive heat generated on a surface of the inkjet printhead.
To achieve a smooth ink-refill balance, a dye or a pigment in the channel may be improved to have a high fluidity and a stability or an emulsifying agent or a co-solvent may be employed to improve the ink-refill balance. However, when the dye or the pigment is changed, a variation of the color related to the image quality and the durability of the printed image is caused. Thus, it is difficult to improve the fluidity of ink by changing the dye or pigment, without affecting the quality of the printed image.